Process for producing single-oriented silicon steel sheets having a high magnetic induction



N Z 19 SATORU TAGUCHI ETAL I 3,

PROCESS FOR PRODUCING SINGLE-ORIENTED SILICON H STEEL SHEETS HAVING AHIGH MAGNETIC INDUCTION rlled June 22, 1964 7 Sheets-Sheetl FIG. I

Magnetic fluxdensity (Kilogauss) I 5 lllllll i fiLllllllI |1| O] 0.2030.405 2 3 45 I0 20 304050 I00 Exciting effective VA( VOHAmperes/ kg)INVEN TORS.

Saforu Taguchi Akira Sakakura H i fan or/ Takashirpa WWW F MM 3,287,183ORIENTED SILICON 7 Sheets-Sheet 2 N 1 SATORU TAGUCHI ETAL PROCESS FORPRQDUCING SINGLE STEEL SHEETS HAVING A HIGH MAGNETIC INDUCTION FlledJune 22, 1964 Taguchi Sakakura IN VENTORS.

Saforu A kira Hironor/ Takashima Acid soluble AL N 19 SATORU TAGUCHIETAL 3,

PROCESS FOR PRODUCING SINGLE'ORIENTED SILICON STEEL SHEETS HAVING A HIGHMAGNETIC INDUCTION Filed June 22, 1964 7 Sheets-Sheet B (guuss)INVENTORS.

Saforu Taguchi Akira Sakakura Hi ronori Takashi/pa gym/44 Nov. 22, 1966SATORU TAGUCHI ETAL 3,287,183 PROCESS FOR PRODUCING SINGLE-ORIENTEDSILICON STEEL SHEETS HAVING A HIGH MAGNETIC INDUCTION Filed June 22,1964 7 Sheets-Sheet 4 F|G.4 (I) Rolling direction FIG.5 (I) m m E V WRolling direction Taguch/ Saforu Akira Sakakura Hironori Takashi ma LavW 1966 SATORU TAGUCHI ETAL 3, 3

PROCESS FOR PRODUCING SINGLE-ORIENTED SILICON STEEL SHEETS HAVING A HIGHMAGNETIC INDUCTION Filed June 22, 1964 7 Sheets-$heet 5 .FIG.4 (2)Rolling direclion FIG.5 (2) Rolling direcrion NVEN TORS.

Saforu Taguchi Akira Sakakura Hironol i Takashima BY Wm M 1966 SATORUTAGUCHI ETYAL 3,287,183

PROCESS F OR PRODUCING SINGLE-ORIENTED SILICON ISSIfEL SHEETS HAVING AHIGH MAGNETIC INDUCTION 7 Sheets-Sheet 6 Filed June 22,

Rolling direcfion FIGS (3) Rolling direcfion 5 m w w m Saforu TaguchiAkira Sakakura H i ronori Takashima BYW W M PM 1966 SATORU TAGUCHI ETAL3,

PROCESS FOR PRODUCING SINGLE-ORIENTED SILICON STEEL SHEETS HAVING A HIGHMAGNETIC INDUCTION Filed June 22, 1964 7 Sheets-Sheet 7 (gcuss) [9000IBOOO f ITOOO Annealing temperature (C) before final cold-rolling IN VEN TORS.

Saforu Taguchi Akfra Sakakura Hironori Takashima BYWMJL, M

United States Patent PROCESS FOR PRODUCING SINGLE-ORIENTED SILICON STEELSHEETS HAVING A HIGH MAG- ,NETIC INDUCTION Satoru Taguchi, AkiraSakakura, and Hironori Takashima, Kitakyushu, Fukuoka, Japan, assignorsto Yawata Iron & Steel Co., Ltd., Tokyo, Japan, a corporation of Ja an PFiled June 22, 1964, Ser. No. 376,627

4 Claims. (Cl. 148-111) This invention relates to processes forproducing silicon steel sheets and more particularly to a process forproducing single-oriented silicon steel sheets having a high magneticinduction.

Single-oriented silicon steel sheets are to be used mostly as iron coresfor transformers and other electric devices. For their magneticcharacteristics, excitation characteristics (the relation between theintensity of the magnetic field and the magnetic induction) and coreloss characteristics (the relation between the magnetic induction andthe core loss value) must be favorable. The excitation characteristicsare determined depending on the magnitude of the magnetic inductioninduced in the iron core by the given intensity of the magnetic field.For example, the magnetic induction generated in the iron core by theintensity H= (0e) of the magnetic field is represented as B With theiron core high in B a small ampere turn will do to generate the samemagnetic induction and therefore the electric device can be made small.

The core loss is an energy loss lost from the iron core in case aprescribed alternating current magnetic induction is given to the ironcore. Therefore, the core loss should be as small as possible. In thecase of singleoriented silicon steel sheets, the core loss in the caseof 50 cycles and an alternating current magnetic induction of 15,000gausses is represented with W /50.

More than about 70% of the cost of production of a transformer is saidto be the material cost. It is therefore advisable to reduce thematerial cost by making the transformer as small as possible. I

Generally, in order to reduce the weight of the iron core of an electricdevice, the iron core must be used in a place where the magneticinduction is high. However, a large exciting electric power will berequired therefor, thus the exciting electric power will become largerthan the advantage obtained by the reduction of the weight of the ironcore and the problem caused thereby will be larger.

Further, if the iron core is used in a place where the magneticinduction is high, the core loss value will quickly increase and theincrease of the core loss caused by using the iron core in the placewhere the magnetic induction is high will be larger than the decrease ofthe core loss by the reduction of the weight of the core. Therefore,today, unless an iron core material excellent in excitationcharacteristics (high in the value of B can be produced, the weightreduction and therefore the material cost reduction of an electricdevice will not be able to be expected. Consequently, the supply ofsingle-oriented silicon steel sheets high in B is strongly desired byelectric manufacturers.

Now, in order to improve the magnetic property of a single-orientedsilicon steel sheet, it is necessary first to highly arrange in therolling direction the l00 axis of the crystal grains forming the steelsheet and second to reduce the impurities in the final product to be aslittle as possible.

Since a process for producing single-oriented silicon steel sheets bytwo-step rolling was invented by N. P. Goss, numerous improvements andsuggestions have been made and the magnetic induction and core lossvalue have ice been improved year after year. In recent years, due tothe development of steel making, surface treating and annealingtechniques, the core loss value has become considerably lower. However,the improvement of the magnetic induction B may be said to be in asaturated state. Even the so far reported highest value is, as shown inUS. Patent No. 2,867,557, B =18,690 gausses at the maximum, ranging from17,610 to 18,690 gausses and averaging 18,090 gausses.

An object of the present invention is to provide a product far superiorin magnetic characteristics to any conventional single-oriented siliconsteel sheet.

Another object of the present invention is to provide a process forproducing single-oriented silicon steel sheets of a high magneticinduction showing B of at least 18,000 gausses and 19,100 gausses at themaximum.

Other objects of the present invention and the substance of theinvention will be able to be more completely understood with referenceto the following specification and claims together with the accompanyingdrawings in which:

FIGURE 1 is a diagram showing excitation effective volt-ampere curves ofa typical product A of 'the present invention and a typical product B ofa conventional single-oriented silicon steel sheet;

FIGURE 2 is a diagram showing a relation between the content ofacid-soluble Al and S in an ingot and the magnetic induction B in therolling direction of the product;

FIGURE 3 is a diagram showing a relation between the combination ofcold-rolling reduction in thickness and the magnetic induction B in therolling direction of the product;

FIGURE 4 shows (110) pole FIGURES 1 and 2 and a pole FIGURE 3 showingthe crystal orientation after each annealing step in case a product isobtained in the typical treating step of the present invention;

FIGURE 5 shows pole FIGURES 1 and 2 and a 100) pole FIGURE 3 showing thecrystal orientation after 'each annealing step in case a product isobtained in a conventional typical treating step for producingsingleoriented silicon steel sheets;

FIGURE 6 is a diagram showing a relation between the temperature ofannealing carried out just before the final cold-rolling step and themagnetic induction B in the rolling direction of the product.

According to the present invention, a silicon steel material ofspecified contents of such elements as C, S and acid-soluble Al ishot-rolled to be a hot-rolled sheet, which is further subjected tospecial cold-rolling and annealing different from conventional ones tobe a product. That is to say, in the process, the thickness of the finalproduct is obtained by at least more than one annealing step and atleast one or more cold-rolling steps. Especially there is a feature thatthe reduction in thickness in the final coldrolling is so high as to bein the range of 81 to 95% and that the reduction in thickness in othercold-rolling steps than the final cold-rolling step is kept to be in therange of 5 to 40%. The two annealing steps to be carried out after thefinal cold-rolling, that is, the annealing at such low temperature as750 to 850 C. to give a primary recrystallization texture to a steelsheet and to decarburize it and the annealing at such high temperatureas above 1000 C. for a long time to produce expected secondaryrecrystallization grains of the (110) [001] orientation may be carriedout in the same manner as in the generally known art. To be specified inthe annealing step in the present invention is the annealing conditionbefore the final cold-rolling (the final intermediate annealingcondition). That is to say, before this annealing is carried out, thesteel sheet must contain 0.020 to 0.080% C. and the annealing should becarried out at such high temperature as 950 to 1200 C. After thisannealing, AlN must be 3 formed in the steel sheet, and the content ofAlN must be such that N as AlN (N bound in the form of AlN) is more than0.0020%.

By treating the hot-rolled sheet of such composition as has beendescribed above by cold-rolling and annealing conditions quite differentfrom conventional ones, there can be produced a single-oriented siliconsteel sheet in which the parallelism between the rolling direction andthe [001] direction of the crystallization grains is very favorable andin which therefore the magnetic induction is very high. As shown inFIGURE 1, the product A obtained by the present invention is superior inthe excitation characteristics specifically at a magnetic inductionabove 15,000 gausses to the conventional singleoriented silicon steelsheet B.

The present invention shall now be explained in detail in the following.

The silicon steel material which is a starting material in the presentinvention means an ingot made by solidifying by any casting method amolten steelmade by such a steel making method which is an already knownart' as, for example, by an open-hearth furnace, electric furnace orconverter or melted by such a known melting method as, for example, by ahigh frequency electric furnace or vacuum melting furnace. A slabbyingot obtained by a continuous casting method, which recently came intowide use, can be also used as a material in the present invention. Theatmosphere in the case of casting is usually of air but may be vacuum orof an inert gas as well.

As described above, the material in the present invention may be made byany steel making, melting and casting methods. But the composition ofthe material must satisfy the following conditions, irrespective of themethod for producing the same. The material (which shall be known as theingot hereinafter) must contain 0.025 to 0.085% C, 2.5 to 4.0% Si, 0.010to 0.065% acid-soluble Al and 0.005 to 0.050% S, the rest being iron andmixed impurities. The acid-soluble Al so called here designates Alsoluble in a dilute sulphuric acid solution of 1 part of sulphuric acidto 9 parts of water and is, to be concrete, a total of Al in asolid-solution in the silicon steel and such nitride of Al as AlN. Theacid-insoluble Al means such Al oxide as A1 It is needless to say thatthe sum total of acid-soluble Al and acid-insoluble Al is total Al.

As described above, the present invention is characterized by the stepsof hot-rolling a silicon steel ingot of specified contents of C, Si,acid-soluble Al and S so as to be a hot-rolled sheet, cold-rolling theabove mentioned hot-rolled sheet at a reduction in thickness of 5 to40%,

thereafter annealing the cold-rolled sheet at such high temperature as950 to 1200 C. so that AlN having such a size as will markedlyfacilitate the production of secondary recrystallization grains of the(110) [001] orientation may be precipitated, cold-rolling the annealed.sheet at a reduction in thickness of 81 to 95% and subjecting the thusobtained sheet -to known annealings for decarburization and secondaryrecrystallization.

That is to say, if the contents of C, Si, acid-soluble Al and S in thesilicon steel ingot are specified as in the present invention and theannealing before the final cold-rolling is carried out at such hightemperature as 950 to 1200- C. for 30 seconds to 30 minutes, AlN havingsuch a size as can produce secondary recrystallization grains of' the(110) [001] orientation in which the parallelism between the l00 axisand the rolling direction is very excellent will be able to beprecipitated as more than 0.0020% N as AlN. Only in case such a steelsheet is finally coldrolled at such a high reduction in thickness as isspecified in the present invention, the object of the present inventionwill be able to be attained. In case any one of the elements of thecomposition deviates from the specified range or in case the temperatureand time of the final annealing do not conform to the specifiedconditions, it will be impossible to precipitate the specified amount ofV 4 AlN having such a size as will produce secondary recrystallizationgrains of the (110) [001] orientation in the steel sheet before thefinal cold-rolling, whereby the object product will not be obtained.

As in the above, in the present invention, the three conditions of thecomposition, the annealing carried out just before the finalcold-rolling and the final cold-rolling are closely related with oneanother. By the treating steps having such three conditions, there canbe obtained a product far superior in magnetic characteristics to anyconventional single-oriented silicon steel sheet.

The reasons for specifying the composition of the ingot in the presentinvention shall be explained in the followmg.

A silicon steel ingot which contained about 3% Si and 0.040% C and inwhich the contents, of acid-soluble Al and S varied as shown in FIGURE 2was rolled while hot to be a hot-rolled sheet 3 mm. thick. The contentof: C in the hot-rolled sheet was 0.040% The sheet was first cold-rolledat a reduction in thickness of 30%, was then annealed at 1100 C. for 5minutes, was finally cold-rolled at a reduction in thickness of 85.7% tobe of a final gauge of 0.3 mm., was then decarburized at 800 C. and wasfinally box-annealed at 1200" C. The relation between the magneticinduction B of the thus obtained product and the acid-solubleAl and S inthe ingot is shown in FIGURE 2. That is to say, the magnetic induction Bof the final product obtained by the producing steps according to thepresent invention is greatly different depending on the contents of Sand acid-soluble Al. As evident from this diagram, the object product ofthe present "invention in which the magnetic induction B in the rollingdirection is higher than 18,000 gausses will be obtained when theacid-soluble Al is 0.010 to 0.065% and S is 0.005 to 0.050%. I As shownby the curve of the magnetic induction B in FIG. 2 the addition eflectof S and acid-solubleAl is determined by the following formula of theaddition ratio of both components:

In this formula as is to be made the value ranging from 0.025 (straightline A in FIG. 2) to 0.015 (straight line B in FIG. 2). It is mostpreferableto contain S and acid-soluble A1 in such a ratio that a may beabout 0.010

(straight line C in FIG. 2) in the above formula, when t andacid-soluble Al is less than 0.010% or more than 0.050%, the productionof secondary recrystallization grains of the [001] orientation in thefinal annealing will become remarkably low and the magnetic induction Bin the rolling direction of .the final product will not exceed 18,000gauses, even if-the addition ratio of S and acid-soluble Al would belimited in the range as mentioned in the above formula. For the abovedescribed reasons, the composition of the silicon steel ingot to be usedin the present invention should be so specified that S be in the rangeof 0.005 to 0.050%, acid-soluble Al in the range of 0.010 to 0.050% andmoreover in the addis(%) acid-soluble Al( +0;

a be in the range of 0.025 to 0.015.

Si is specified to be in the range of 2.5 to 4%. In case it is less than2.5%, there will be a disadvantage that the electric resistance will beso low and the eddy current loss will be so high that the core lossvalue will be high. On the contrary, in case Si is more than 4%, breaksdue to brittleness will be caused in cold-rolling. Therefore, in thepresent invention, the content of silicon in the silicon steel ingot isdefined to. be 2.5 to 4%,

It was shown that in this case the magnetic,

However, as seen in FIGURE 2, even if a silicon steel ingot in which Si,acid-soluble Al and S are in the above mentioned specified ranges istreated, the magnetic induction B of the final product will not exceed18,000 gausses in some case. Taking such a case into consideration, afurther condition of composition must be specified. It is the content ofaluminium nitride or AlN. This AlN must be precipitated in the steelsheet before the final cold-rolling but need not always be precipitatedin the ingot, because, if the ingot contains Al, the Al will react withN in the steel in the heat-treatment and Will be precipitated as AlN inthe steel. FIGURE 2 shows also a specification of such content of AlN inthe steel sheet be fore the final cold-rolling as is required in thepresent invention. The numeral attached to each point in the diagramrepresents the content of AlN in the steel sheet before the finalcold-rolling in N as AlN in percent by weight 10 As seen from this, incase N as AlN is less than 0.0020%, even if the main elements Si,acid-soluble Al and S in the above mentioned ingot are in the specifiedranges, the magnetic induction B in the rolling direction of the finalproduct will not exceed 18,000 gausses and the object of the presentinvention will not be able to be attained.

For the above reasons, the content of AlN in the steel sheet before thefinal cold-rolling in the present invention must be such that N as AlNis more than 0.0020%.

Now, it has been found to be requisite that AlN having such a size asbeing able to produce secondary recrystallization grains of the(110)[001] orientation should be present in the steel sheet before thefinal cold-rolling, and that such AlN should be precipitated in theannealing step just before the final cold-rolling. The precipitation ofsuch AlN can be attained by adjusting the content of C in the steelsheet before the annealing so as to be at least 0.020 to 0.080% andannealing the steel sheet at 950 to 1200 C. for 30 seconds to 30minutes. It has been confirmed that, in case the content of C in thesteel sheet before the annealing is less than 0.020% or exceeds 0.080%,even if the content of AlN is such that N as AlN is more than 0.0020%,the precipitate size will not be proper and, as a result, secondaryrecrystallization grains of the (110) [001] orientation will not beproduced in the final annealing. Therefore, in the present invention, inorder to adjust the content of C in the steel sheet before the annealingso as to be in the range of 0.020 to 0.080%, it is necessary that thesilicon steel ingot should contain at least 0.025 to 0.085% C, becauseslight decarburization (of about 0.005%) will occur in the hot-rollingof ingot and subsequent annealing of the ingot.

As described above, it has been confirmed that in the present invention,the contents of the four elements in the silicon steel ingot should beso defined as to be 0.025 to 0.085% C, 2.5 to 4.0% Si, 0.010 to 0.065%acid-soluble Al and 0.005 to 0.050% S and that the C content in thesteel before the annealing step immediately antecedent to the finalcold-rolling should be adjusted to be in the range of 0.020 to 0.080% inorder that AlN having such a size as will produce secondaryrecrystallization grains of the (110) [001] orientation may beprecipitated in an amount of at least 0.0020% of N as AlN in saidannealing step. Only when such specifications of the composition and thefinal cold-rolling step at such a high reduction in thickness as isdescribed in the following are closely combined together, it will bepossible to produce a single-oriented silicon steel sheet of a highmagnetic induction.

The concrete steps of one embodiment of the method according to thepresent invention are carried out in the following sequence. After thehot-rolled silicon steel sheet is pickled, it is subjected to acold-rolling, the coldrolled sheet is annealed and the annealed sheet isagain subjected to a cold-rolling by the conventional two annealingsteps, that is, the annealing for decarburization and that for producingrecrystallization grains to obtain a desired final product. Hereinafterthe first cold-rolling will be designated as the first cold-rollingstep, the sequent annealing as the intermediate annealing step, thefollowing cold-rolling as the final cold-rolling step and the annealingfor producing recrystallization grains as the final annealing. Ofcourse, each cold-rolling step may comprise several rolling passes.However, in the present invention the cold-rolling step prior to thefinal cold-rolling step is not limited to only one. It may be repeatedeven several times, combined with the sequent annealing step accordingto conditions. Further, in another embodiment even the firstcold-rolling step may be omitted. In such a case the cold-rolling willbe carried out only in one step (that is, the final cold-rolling step asdesignated here) after the antecedent annealing step. The features ofthe present invention reside in the reduction in thickness in thecoldrolling steps, particularly in the final cold-rolling step and theannealing conditions in the intermediate annealing step immediatelyprior to the final cold-rolling step.

First of all, the cold-rolling condition will be explained.

Silicon steel ingots made by melting in an electric furnace and castingand containing 0.040% C, 3.02% Si, 0.031% acid soluble Al and 0.030% Swere bloomed, hot-rolled and finished to be hot-rolled sheets 7.0, 5.0,3.4, 3.0, 2.6 and 1.8 mm. thick. The content of C in each hot-rolledsheet was about 0.040%. By using each sheet as a starting material, thefirst cold-rolling step was carried out at a reduction in thickness of 0to as shown in the lower part in FIGURE 3. (In this case, 0 was notsubjected to the first cold-rolling step and was therefore subjected toonly one final cold-rolling'step.) The sheet was then annealed at 1100C. for 5 minutes, was then subjected to the second cold-rolling step(final cold-rolling step) at the reduction in thickness also shown inthe lower part of the diagram so as to be of a final thickness of 0.3mm., was decarburized in wet hydrogen at 800 C. for 5 minutes and wasfinally box-annealed at 1200 C. for 20 hours. The relation between themagnetic induction B of the thus obtained product and the reduction inthickness is shown in FIGURE 3. The facts evident from this diagram arethe following two points. It has been found that the reduction inthickness in the final cold-rolling step required for the magneticinduction B in the rolling direction of the product to exceed 18,000gausses should be at least 81%, but not exceed and is most preferably inthe range of 83 to 92% and that the reduction in thickness in the firstcold-rolling step should be kept less than 40%. However, in case thefirst coldrolling step is carried out at a reduction in thickness notexceeding 5%, the effect On the improvement of the magneticcharacteristics of the product will not be more remarkable than in thelater described case of making the final product thickness in only onecold-rolling step, that is, in the case of omitting the firstcold-rolling step. Thus, in such a case it will be meaningless to carryout the cold-rolling in two steps, which means that the reduction inthickness in the first cold-rolling step should be in the range of 5 to40%.

To sum up, the cold-rolling may be carried out only in one step or intwo steps or even in several steps. In case the cold-rolling is carriedout only in one step, the reduction in thickness should be 81 to 95%.But, in case it is carried out in two or more steps, the followingconditions must be absolutely fulfilled: that is, the final coldrollingstep should be carried out at a reduction in thickness of 81 to 95% andany cold-rolling step prior to the final cold-rolling step at areduction in thickness of 5 to 40%. The cold-rolling treatments at suchspecific reduction in thickness have never been seen in any alreadydisclosed process for producing single-oriented silicon steel sheets.Only in the case of using a silicon steel ingot of the above specifiedcomposition contents, such cold-rolling treatments will be significant.

The silicon steel sheet to be used as an iron core for electric devicesis mostly about 0.3 mm. thick. When such a final sheet thickness is tobe obtained with two cold-rolling steps and one annealing step, it willbe most preferable that the thickness of the hot-rolled sheet is 2.6 to3.4 mm. However, in case the thickness of the hot-rolled sheet is 7 mm.a product high in magnetic induction will be hardly obtained with twocold-rolling steps only. In such a case, the cold-rolling at a reductionin thickness of to 40% and the annealing are repeated several times,followed by the final intermediate annealing and the final cold-rollingto obtain a product of a high magnetic induction comparable to that ofthe former.

In the present invention, irrespective of the sheet thickness of thefinal product, a product high in magnetic induction may be obtained.However, usually, if the thickness of the hot-rolled sheet is more than7 mm., it is difficult to wind the sheet to be in the form of a coil orto strip and cold-roll it. Further, it is difficult in the hot rollingtechnique to make a hot-rolled sheet less than 1.5 mm. thick. Therefore,for factory conditions, it is defined that in case two or morecold-rolling steps are included the sheet thickness should be 1.5 to 7mm.

Though the theoretical ground of the cold-rolling treatment in thepresent invention is not apparent, a clear difference from anyconventional cold-rolling treatment can be perceived from theobservation of the crystal orientation. FIGURES 4 and 5 show with (110)and (100) pole figures the crystal orientations obtained after carryingout the respective annealing in the products corresponding to A (of B of19,100 gausses) and B (of B of 17,600 gausses) in FIGURE 3,respectively.

From the above figures it is evident that the crystal orientation shownafter carrying out the decarburization annealing is quite differentbetween the case of carrying out the cold-rolling treatments (atreduction in thickness of in the first cold-rolling step and 87.5% inthe final cold-rolling step) according to the present invention and thecase of carrying out the conventional cold-rolling treatments (atreduction in thickness of 70% in the first cold-rolling step and 66.7%in the final cold-rolling step).

FIGURES 4 1 and 5 1 are (110) pole figures after the respectiveintermediate annealings (at 1100 C. for 5 minutes in the former and at1100 C. for 5 minutes in the latter). FIGURES 4 2 and 5 2 are (110) polefigures after the decarburizing annealings (at 850 C. for 5 minutes inboth). FIGURES 4 3 and 5 3 are (100) pole figures after the finalannealings (at 1200 C. for 20 hours in both). The numerals in FIG. 4 1and 2, and FIG. 5 1 and 2 designate the strength of crystal orientationas compared with that of random crystal orientation in the X-raydiffraction as the standard value, taking the latter as 1.0 and those inFIG. 4 3 and FIG. 5 3 the grain numbers of the secondaryrecrystallization grains.

As described later, the decarburizing annealing is carried out to removeC detrimental to the development of secondary recrystallization grainsof the (110) [001] orientation in the final annealing and at the sametime to make the cold-rolled structure a primary recrystallizationstructure. The primary recrystallization orientation (FIGURE 5 2) afterthe decarburizing annealing in the case of carrying out the conventionalcold-rolling treatment is a main orientation rotated by about degreesaround the 110 rotation axis parallel with the rolling direction withthe (100) [001] orientation as a center. On theother hand, the crystalorientation (FIGURE 4 2) after the decarburizing annealing in the caseof carrying out the cold-rolling treatment according to the presentinvention has a feature that the 110 rotation axis is deviated by about20 to 25 degrees to right and left from the rolling direction. Theparallelisms between the 100 axis of the secondary recrystallizationgrains of the (100) [001] orientation produced when both of them werefinally annealed and the rolling direction are as respectively shown by(100) pole figures in FIGURES 4 3 and 5 3. The former is remarkablysuperior in the 3 and thereafter subject the thus obtained sheet toknown annealings for decarburization and secondary recrystallization.However, in this case the thickness of the hotrolled sheet must be 1.5to 5 mm.

The annealing step shall now be described. First of all, the conditionsof the intermediate annealing step iIII'. mediately prior to the finalcold-rolling step, which make one of the most important features in thepresent invention, shall be described. A silicon steel ingot prepared bymelting in an electric furnace and casting and containing 0.038% C, 3.0%Si, 0.030% acid-soluble Al and 0.028% S was bloomed and hot-rolled to bea hotrolled sheet having a thickness of 3.0 mm. The content of C in thehot-rolled sheet was 0.037% The sheet was coldrolled by 30%, was thenannealed in H at temperatures of 800, 900, 950, 1000, 1050, 1100, 1150,1200 and 1300 C. for 5 minutes each, Was then finally cold-rolled at areduction in thickness of 85.7% to be of a product thickness, wasannealed to be decarburized at 800 C. for 5 minutes and was then finallyannealed in H at 1200 C. for 20 hours. The relation between the magneticinduction B in the rolling direction of the product and the annealingcondition before the final cold-rolling is shown in FIGURE 6.

It is understood from this that the annealing tempera- I ture to obtaina product of a magnetic induction B of 18,000 gausses in the rollingdirection as desired in the present invention must be in the range of950 to 1200 C. and that the most preferable temperature range is 1050 to1150 C. The annealing time in this temperature minutes.

the time exceeds 30 minutes, the crystal grains will grow,

after the recrystallization has been completed, resulting in anincomplete development of the secondary recrystallization grains of the[001] orientation in the final annealing in both cases. As alreadydescribed, the atmosphere for the annealing has nothing to do with theprecipitation of AlN in the steel sheet before the final cold-rollingstep. Usually, in case the silicon steel ingot is made in an open-hearthfurnace or the like, the ingot as it is will contain more than 0.0040% Nwhich will further increase in the hot-rolling. Therefore, AlN havingthe desirable size will be able to be precipitated as more than 0.0020%N as AlN'by subjecting the steel sheet to the intermediate annealingimmediately prior to the final cold-rolling step, even if nitrogen isnot specifically added in this annealing, provided that the content of Cin the steel sheet is being kept in the range of 0.020 to 0.080% asalready specified. Hence, any of reductive and neutral atmospheres suchas, for example, of H Ar and N gases or mixtures of them may be used forthe atmospherefor the annealing. 'However, in case the silicon steelingot is made by melting in a vacuum melting furnace or the like or bycasting by a vacuum casting method or the like, N in the ingot will beso little that, unless nitrogen is added in the annealing before thefinal cold-rolling, it will be impossible to precipitate more than0.0020% N as AlN. The method of adding nitrogen. is not specified. But,in the present invention, it is recommended to carry out the annealingin a neutral or reductive gas containing at least 10% by volume N Thereason Why the annealing immediately prior to the final cold-rollingstep in the present invention is carried out at a temperature higherthan in the annealing in any conventional process for producingsingleoriented silicon steel sheets is presumed to be that, on accountof C contained in the steel sheet before being subjected to theannealing the my transformation will oc-cur in this range of annealingtemperature and the precipitation of AlN having such a size as willfacilitate the production of secondary recrystallization grains of the(110) [001] orientation will be accelerated thereby. It is consideredthat such AlN together with the subsequent final cold-rolling treatmentat a high reduction in thickness and annealing treatment will make itpossible to produce nuclear crystal grains of the (110)[ 001]orientation very excellent in; the parallelism between the 100 axis andthe rolling direction. In case the intermediate annealing is to berepeated between several coldrolling steps before the final intermediateannealing, it may be carried out at such temperature and for such timeas are sufficient to make the cold-rolled structure (obtained bycold-rolling) a primary recrystallization structure.

The steel sheet finally cold-rolled to be of a product sheet thicknessis then subjected to the carburizing annealing. This annealing is tomake the cold-rolled structure a primary recrystallization structure andat the same time to remove C detrimental to the development of secondaryrecrystallization grains of the (110)[001] orientation in the finalannealing. For the decarburizing method may be used any known method.For example, there can be enumerated a method of annealing in wethydrogen at a temperature of 750 to 850 C. for a short time.

The final annealing should be carried out at such temperature and forsuch time that secondary recrystallization grains of the 110) [001]orientation can Well develop. In order that the secondaryrecrystallization grains may perfectly develop, the steel sheet must beannealed at a temperature higher than 1000 C. for at least hours. Evenif the atmosphere for the final annealing is a neutral or reductiveatmosphere or such Weakly oxidative atmosphere as will not remarkablyoxidize the steel sheet, the object product of the present invention inwhich the magnetic induction B in the rolling direction is more than18,000 gausses Will be obtained. However, in order to reduce the coreloss value, it is usually recommended to finally anneal the steel sheetin H2.

Example I A silicon steel ingot containing 0.037% C, 3.00% Si, 0.028%acid-soluble Al and 0.031% S was prepared in an electric furnace, wasbloomed and was hot-rolled to be a hot-rolled sheet 3 mm. thick. Thecontent of C in the hot-rolled sheet was 0.036%. The sheet was firstcold-rolled by 30% and Was then annealed in H at 1100 C. for 5 minutes.

The content of AlN in the steel sheet after the annealing was 0.0049% Nas AlN. The sheet was then coldrolled by 85.7% to be of a product sheetthickness of 0.3 mm., was decarburized in wet hydrogen at 800 C. for 5minutes, was pickled and was finally annealed in hydrogen at 1200 C. for20 hours.

The magnetic characteristics in the rolling direction of the productwere as follows:

B =19,070 gausses W /50 (core loss value at 15,000 gausses at 50 cycles)=0.99 watts/kg.

W 17/50 (core loss value at 17,000 gausses at 50 cycles) 1.30 watts/kg.

Thus a very excellent single-oriented silicon steel sheet Was obtained.

Example 2 A silicon steel ingot containing 0.035% C, 3.00% Si, 0.037%acid-soluble Al and 0.036% S was prepared in an electric furnace, wasbloomed and was hot-rolled to be a hot-rolled sheet 5 mm. thick. Thesheet was coldrolled by 30%, was annealed at 900 C. for 2 minutes so asto be recrystallized and was then again cold-rolled by 30%. At thistime, the content of C in the steel sheet was 0.031%. The sheet was thenannealed in H at 1100 C. for 5 minutes. The content of AlN in the steelsheet after the annealing was 0.0046% N as AlN.

The sheet was then cold-rolled by 87.8% to be of a product sheetthickness of 0.3 mm., was decarburized in wet hydrogen at 800 C. for 5minutes and was finally annealed in H at 1200" C. for 20 hours. Themagnetic characteristics in the rolling direction of the product were asfollows:

B 19,000 gausses W 15/5-0=1.01 watts/kg. W 17/50=1.31 watts/kg.

Example 3 A silicon steel ingot containing 0.040% C, 3.02% Si, 0.030%acid-soluble Al and 0.030% S was prepared in an electric furnace, wasbloomed and was hot-rolled to be a hot-rolled sheet 3 mm. thick. Thecontent of C in the hot-rolled sheet was 0.040%. It was annealed in H at1050 C. for 5 minutes.

The content of AlN in the steel sheet after the annealing was 0.0055 Nas AlN. The sheet was then cold-rolled at a reduction in thickness of89% to be of a product sheet thickness of 0.33 mm., was decarburized inwet hydrogen at 800 C. for 5 minutes and was finally annealed inhydrogen at 1200 C. for 20 hours.

The magnetic characteristics in the rolling direction of the productwere as follows:

B =l8,800 gausses W 15/50 (core loss value at 15,000 gausses at 50cycles)=1.05 watts/kg.

W 17/50 (core loss value at 17,000 gausses at 50 cycles)=l.35 Watts/kg.

What is claimed is: 1. A process for producing single-oriented siliconsteel sheet of (110) [001] orientation, in which a silicon steel ingotcomposed of 0.025 to 0.085 wt. percent C, 2.5 to 4.0 wt. percent Si,0.010 to 0.050 wt. percent acid-soluble Al and 0.005 to 0.050 wt.percent S and the rest being iron is hot-rolled to produce a hot-rolledsteel sheet, said hotrolled steel sheet is subjected to an annealing andcoldrolling to obtain a steel sheet of final thickness, said steel sheetof final thickness is thereafter subjected to an annealing fordecarburization and further for secondary recrystallization, comprisingthe steps of hot-rolling a material, in which the ratio of S andacid-solution Al is made to be S( acid-soluble A1(%)+0.025 to 0.015

to make the thickness of said material to 1.5 mm. to 7 mm., cold-rollingthe thus hot-rolled steel sheet at a reduction in thickness of 5 to 40%,annealing the coldrolled sheet at a temperature ranging from 950 to 1200C. for 30 seconds to 30 minutes and then finally cold-rolling the thusannealed steel sheet at a reduction in thickness of 81 to 2. A processfor producing single-oriented silicon steel sheet claimed in claim 1, inwhich a material, in which the ratio of S and acid-soluble Al is made tobe acid-soluble Al( +0.010 is subjected to a hot-rolling.

3. A process for producing single-oriented silicon steel sheet claimedin claim 1, in Which a cold-rolled steel sheet containing 0.020 to 0.080wt. percent C is annealed at a temperature ranging from 950 to 1200 C.for 30 seconds to 30 minutes and thereafter the thus annealed steelsheet is finally cold-rolled.

4. A process for producing single-oriented silicon steel sheet claimedin claim 1, in which a material is hot-rolled to make the thickness ofsaid material to 1.5 to 7 mm., the thus obtained steel sheet is thenannealed at a temperature ranging from 950 to 1200" C. for 30 seconds to30 minutes and the thus annealed steel sheet is cold-rolled at areduction in thickness of 83 to 96%.

No references cited.

DAVID L. RECK, Primary Examiner.

N. F. MARKVA, Assistant Examiner.

1. A PROCESS FOR PRODUCING SINGLE-ORIENTED SILICON STEEL SHEET OF (110)001! ORIENTATION, IN WHICH A SILICON STEEL INGOT COMPOSED OF 0.025 TO0.085 WT. PERCENT C, 2.5 TO 4.0 WT. PERCENT SI, 0.010 TO 0.050 WT.PERCENT ACID-SOLUBLE AL AND 0.005 TO 0.050 WT. PERCENT S AND THE RESTBEING IRON IS HOT-ROLLED TO PRODUCE A HOT-ROLLED STEEL SHEET, SAIDHOTROLLED STEEL SHEET IS SUBJECTED TO AN ANNEALING AND COLDROLLING TOOBTAIN A STEEL SHEET OF FINAL THICKNESS, SAID STEEL SHEET OF FINALTHICKNESS IS THEREAFTER SUBJECTED TO AN ANNEALING FOR DECARBURIZATIONAND FURTHER FOR SECONDARY RECRYSTALLIZATION, COMPRISING THE STEPS OFHOT-ROLLING A MATERIAL, IN WHICH THE RATIO OF S AND ACID-SOLUTION AL ISMADE TO BE